feat(qb): implement relation logic

apps/web/src/components/onboarding/onboarding.tsx

libs/shared/lib/data-access/store/querybuilderSlice.ts

libs/shared/lib/querybuilder/model/graphology/utils.ts

libs/shared/lib/querybuilder/panel/querybuilder.tsx

...rybuilder/pills/customFlowPills/entitypill/entitypill.tsx

...r/pills/customFlowPills/relationpill/relation-handles.tsx

...ilder/pills/customFlowPills/relationpill/relationpill.tsx

.../querybuilder/pills/pilldropdown/pilldropdown.module.scss

...ybuilder/pills/pilldropdown/pilldropdown.module.scss.d.ts

...ared/lib/querybuilder/pills/pilldropdown/pilldropdown.tsx